Agricultural and urban land uses often contribute to nonpoint source pollution of lakes and streams resulting in impairment of fisheries, recreational areas, and public waterways. Methods of reducing pollution using conventional treatment methods usually used to reduce pollution from point sources such as sewage outlets and disposal outlets carrying industrial wastes are inappropriate for us in treating nonpoint source pollution such as runoff from fields and golf courses.
The use of constructed wetlands in water pollution control has been known. Constructed Wetlands for Wastewater Treatment by Donald A. Hammer (Lewis Publishers, 1989) gives an overview of use of constructed wetlands for control of pollution from municipal, industrial and agricultural sources. Among the constructs disclosed therein is a wetland system that uses a "debris basin" to retain gross debris and serves as a distribution structure which then discharges stormwater runoff to a parkland and wildlife habitat area that eventually drains into a bay. The system works primarily to detain water for controlled distribution to the parkland area. The construct does not provide for sediment collection or for treatment of runoff by passage through the system comprising a grass filter and a constructed wetland as disclosed herein.
In another chapter, Hammer describes a method for treatment of stormwater runoff from a shopping mall. The water was collected in two separate basins, then directed through a box culvert to a wet detention pond and, finally, through a series of wetland basins The system lacks several components of the instantly disclosed construct. For example, the level-lip spreader and grass filter are not seen in that disclosure. That construct as taught by Hammer is not appropriate for use in control of runoff from golf courses or fields.
In yet another use of constructed wetlands disclosed in Hammer, the wetland was used to treat landfill leachate. The construct disclosed therein differs substantially from that of the present invention. That construct required collection of the leachate in ranks for dispersal into the treatment area. That construct lacked the grass filter, level lip spreader and deep pond used in the present construct. That construct taught by Hammer would not be appropriate for use in control of non-point source pollution such as runoff from fields.
In 1990 a compilation of papers was prepared for inclusion in a publication distributed at an International Conference on Use of Constructed Wetlands in Water Pollution Control. While some of the components of the instantly disclosed invention were used by the authors, none of the constructs combined the use of the sediment basin, level lip spreader and grass filter in the manner of the invention.
Some teachings regarding use of planted constructs to control pollution and erosion are seen in the patent literature. U.S. Pat. No. 4,345,856 to Tuck discloses the use of a combination of rip rap, loam and plantings. No pollution controlling wetlands are constructed.
U.S. Pat. No. 4,839,051 to Higa discloses a means of treating contaminated water requiring dispersal of water from a tank into an area that has been planted with plants of differing root lengths. No sediment basin, level-lip spreader, or grass filter is disclosed therein. The method would not be appropriate for control of nonpoint source pollution.
U.S. Pat. No. 4,995,969 to LaVigne discloses a living filter system for treatment of sanitary landfill leachate. The construct comprises a treatment basin lined with a water-impervious material and planted with leachate-toleran plants growing in the treatment medium. The leachate is applied to the system from a tank. No sediment basin or grass filter is seen disclosed therein.
In 1988 the Environmental Protection Agency, Office of Research and Development, published a design manual for constructed wetlands and aquatic plant systems for municipal wastewater treatment. That manual did not disclose the use of the level-lip spreader and grass filter or the deep pond as used in the system described herein. The system was primarily concerned with the use of wetland plants such as cattails, bulrushes, and reeds. The effluent was supplied to the system through a pipe and pumping system.